Process of obtaining hydrogen sulphide



J. A. SHAW PROCESS OF OBTAINING HYDROGEN SULPHIDE Jan. 14, 1936.

Filed Jan. 8, 1932 g/osqob Al/70u): B Y Q l A 301211122'.

Patented Jau. 14, 1936 PATENTl OFFICE PROCESS F OBTAINING HYDROGEN r SULPHIDE Joseph A. Shaw, Pittsburgh, Pa., assigner to The Koppers Company of Delaware, a corporation of Delaware Application January 8, 1932, Serial No. 585,410

6 Claims.

s My invention relates to hydrogen sulphide and has among its objects the provision of a process for obtaining hydrogen sulphide in substantially pure form, uncontaminated by other gases of a l deleterious character and suitable for use for the preparation of sulphur dioxide to be used in the manufacture of sulphuric acid and for other purposes in which hydrogen sulphide of a high degree of purity is required.

In addition to the general object recited hereinabove my invention has for objects such other operative advantages and improvements as may h'ereinafter be found to obtain.

In my copending application Serial No. 570,961, filed October 24, 1931, of which this application is a continuation-in-part, there is described and claimed a process for the separation and purification of gaseous mixtures containing hydrogen sulphide and analogous acidic gases which com- 20 prises recirculating a solution containing a phenolate Athrough a cycle comprising an absorption stage in which it is brought into contact with the gaseous mixture to be separated or puried and an actication stage in which impurities or 25 constituents absorbed from said gaseous mixtures are liberated by heating the solution.

Many sources of hydrogen sulphide in gaseous form contain, in addition to hydrogen sulphide, varying amounts of carbon dioxide. While, from 30 the standpoint of gas purification an incidental removal of carbon dioxide is ordinarily not ob-` jectionable, the presence of carbon dioxide may yconstitute a distinct disadvantage from the standpoint of recovering hydrogen sulphide.

3,5 Thus Where the hydrogen sulphide is to be burned -to sulphur dioxide and the sulphur dioxide then employed for the manufacture of sulphuric acid, the presence of carbon dioxide is undesirable, probably for the reason that carbon dioxide tends' 40 in some way to reduce the activity of or destroy oxides of nitrogen necessarily present in the manufacture of sulphuric acid.

As carbon dioxide is of more strongly acidic character than hydrogen sulphide, it would or- 45 dinarily be expected that, when a mixture of tnese two gases is subjected to the action of an a1- kaline absorbent solution, absorption of carbon dioxide will take place in preference to absorption of hydrogen sulphide.

50 However, this is not the case. It has been found that a solution of the character indicated accomplishes a preferential absorption of HzS as '1* compared with CO2.` This results in a marked increase in the HzS to CO2 ratio of the gases lib- 55 e1 itedin the actication stage. In certain in- (Cl. ,Z3-181) stances, the amount of CO2 thus liberated falls to substantially nil, and there is recovered either substantially pure HzS or H25 so nearly pure as to make feasible the separation of small amounts of CO: therefrom. Y 5

Thus, when a gas containing substantially equal quantities of carbonmdioxide and hydrogen sulphide was treated with a sodium phenolate solution or other solution capable of regeneration by heat in the absence of carbon dioxide, and was then heated to drive oi the absorbed hydrogen sulphide, the gases liberated in the heating or actifying stage comprised not less than 90% HzS and not more than 10% CO2.

When the gaseous mixture treated contained at least twice as much HzS as C02, the HzS driven off in the heating or actifying stagewas substantially pure, little or no CO2 being driven off at the same time. y

Consequently one phase of my invention contemplates obtaining hydrogen sulphide in substantially pure form by washing a gaseous mixture containing relatively small amounts of carbon dioxide as compared to hydrogen sulphide and preferably at leasttwice as much hydrogen sulphide as any carbon dioxide which may be present with an absorbent liquid capable of regeneration by heating, preferably a phenolate solution of the character indicated hereinabove and as described in my copending application in which I have said: The concentration of the solution may vary considerably, depending primarily upon the content of acidic gases and the degree of separation and purification desired. But in general I prefer to employ a liquid containing from 5% to 20% by weight of alkali-forming metal calculated as ROH (where R represents an alkali-forming metal), and containing a pheno1, or otherew auxiliary acidic substance either as such or in'icombination with all or a portion of 40 the alkali-forming metal. The molar ratio of the alkali-forming metal present in the form of a compound or compounds having an alkaline reaction to the phenol or the phenolate radical or equivalent may be, for example, from 2:1 to 2:3, 45 calculated as ROH and as free acid, respectively".

My invention further contemplates certain novel methods of obtaining hydrogen sulphide in substantially pure form in instances where the hydrogen sulphide liberated in the` actication stage of a process of the character referred to hereinabove would otherwise contain undesirable amounts of carbon dioxide. I have found that compounds of alkaline earth metals, such for example as calcium hydroxide.

can be used to-accomplish a preferential absorption or retention of carbon dioxide with little or no absorption or retention of hydrogen sulphide, and I utilize this discovery either by supplying a compound of this character, for example, calcium hydroxide, in the form of milk of lime, to

causing the removal or retention of an undesirable amount of the hydrogen sulphide present.

My invention also contemplates the removal from gases liberated in the actication stage or any other constituents such as phenol, the presence of which in the liberated hydrogen sulphideis deleterious or undesirable.

In order that my invention may be fully set forth and understood, I now describe, with reference to the accompanying drawing a preferred manner in which it may be practiced and carried out. In this drawing,

The single figure is a more or less diagrammatic view, partly in elevation and partly in vertical section, of apparatus for carrying out the process of my invention.

Referring to the drawing, an absorbent solution, preferably a solution of an alkali metal phenolate although other alkaline absorbent liquids may be employed, is introduced to an absorber I through an inlet 2 located at or near the top thereof and ilows downward through the absorber I in countercurrent to a rising flow of a gas or gaseous mixture introduced to the bottom of the absorber I through an inlet 3.

The gaseous mixture introduced through the inlet 3 to the absorber I is preferably one containing at least twice as much hydrogen sulphide as any carbon dioxide which may be present and may be obtained from any convenient source of such gas.

During the countercurrent passage of the absorbent liquid and the gaseous mixture the liquid absorbs hydrogen sulphide and may or may not absorb carbon dioxide, according to the amount of carbon dioxide present in the gaseous mixture. The treated gaseous mixture then escapes from the absorber I through an outlet 4 and the liquid containing absorbed hydrogen sulphide, and it may be carbon dioxide also, passes out of the bottom of the absorber I through a conduit 5.

Where the gaseous mixture treated in the absorber I contains insuihcient carbon dioxide in proportion to the amount of hydrogen sulphide present to cause absorption of carbon dioxide in the absorber I to an undesirable extent, the liquid is then transferred through a valved conduit 6 in which is located a pump l to a heat exchanger 8 and then passes through a conduit 9 into the upper portion of an actier I0.

'I'he absorber I and the actiler Ill may both comprise gas-and-liquid contact apparatus of any desired type, althoughni the present instance bell-and-tray type columns of more or less conventional design are preferred, the apparatus illustrated in the drawing being of this character.

The liquid flows down through the actiiier I0, at the bottom of which is located some suitable means for heating the solution reaching the bottom of the actifler. Such heating means may comprise, for example, an indirect steam coil II or a direct steam pipe I2, either one or both of which may be employed. Preferably the heating 5 is carried to such extent that the liquid is carried to its boiling point and considerable quantities of steam are evolved which pass upward through the actifler I0. I

Due to the heating and the countercurrent 10 action of the steam, hydrogen sulphide absorbed in the absorber I is driven out of the liquid and the liquid is thereby regenerated for further absorption of hydrogen sulphide. The regenerated liquid is withdrawn from the bottom of the actil5 lier I0 through a conduit I3 in which is located a pump I4 and is delivered by the latter to the heat exchanger 8 where it gives up a portion of its heat `to the liquid entering the actifier Ill. The partially cooled regenerated liquid then 20 passes through a conduit I5 in which is located a pump I6 to a cooler Il of conventional type and finally passes through the conduit 2 into the upper part of the absorber I, thus completing the cycle of recirculation. l25

The vapors liberated from the absorber I pass upward through a dephelegmator I8 preferably located on top of or above the actiiier I0 which is provided for the purpose of removing phenol volatilized in the latter. Portions of the con- 30 densed liquid reaching the bottom of the dephlegmator I8 may be withdrawn through a conduit 20 and passed by means of a pump 2I through a cooler 22 before being returned through a conduit 23 to the top of the dephlegmator, while ex- 35 cess condensate is returned through a sealed overow 24 to the actiiier I0. In this manner, or by means of any other suitable dephlegmating apparatus, substantially all phenol volatilized in the actifler I0 may be returned thereto and steam -40 present in the vapors leaving the actier I0 may also be condensed and returned to the latter.

The liberated gases leave the top of the dephlegmator I8 through a conduit 25 provided for the removal and collection of the same. When 45 these gases contain unobjectionable amounts of carbon dioxide they may be permitted to pass directly through a valved conduit 26 and a conduit 21 to a combustion chamber 28 of any suitable type. 50

In the combustion chamber 28 the hydrogen sulphide is burned by means of air or oxygen introduced through a valved inlet 29 and the resultant sulphur dioxide gases pass through a conduit 30 to a sulphuric acid plant indicated by 55 the reference numeral 3l. As the details of sulphuric acid plants are well known, no detailed description of the same appears necessary.

Where carbon dioxide is present in the gaseous mixture treated in the absorber I to such extent .60 as to cause continued absorption of carbon dioxide to an undesirable extent, the liquid withdrawn from the absorber I through the con- -duit 4 may be delivered through a valved conduit 33 to an agitator 34 and there mixed with milk 65 of lime or other suitable alkaline earth metal compound supplied from a storage tank 35. Sufficient milk of lime is added to precipitate substantially all carbon dioxide which would otherwise be liberated in the actifler I0 and 70 results in the precipitation of the carbon dioxide as calcium carbonate.

'I'he liquid containing this precipitate is introduced through a conduit 36 in which is located a pump 3l to a filter 38 or other separating de- 75 vice where the insoluble carbonate precipitate is removed. Any suitable separating apparatus, such for example as a filter, a settling tank or a centrifuge, may beemployed for this purpose. The clarified liquid or filtrate leavingthe lter 38 is then delivered by a pump 39 through a conduit 40 to the heat exchanger 3 and eventually passes to the actiiler I as before.

As an alternative method of procedure, I may permit any absorbed carbon dioxide to be volatilized in the actier I0, the gases liberated in the actifler III being subsequently treated to eliminate carbon dioxide. For this purpose thelhydrogen sulphide gases passing through the conduit 25 are conveyed through a valved branch conduit 42 to a purifier 43 through which circulates a solution or suspension of a suitable alkaline earth metal compound, such for example as branch conduit 5I.

. I may provide suitable means located in or associated with the sump 41 for filtering the solution or otherwise removing `the insoluble precipitate of calcium carbonate which is formed by the action of the lime solution or suspension upon carbon dioxide in the purifier 43. The

purified hydrogen sulphide passes from the purip fier 43 throughs. conduit 52 and conduit 21 to the combustion chamber 23.

In adding the milk of lime or other precipitant to the agitator 34 or to the purifier 43, I prefer to add an amount of th'e same only suillcient to cause the precipitation of substantially all of the undesirable carbon dioxide which may be present. tained but this amount can be reduced to a substantially negugible amount by thus limiting the amount `of precipitant supplied.

It is of considerable advantage to have the gaseous mixture treated in the absorber I under `more than atmospheric pressure as this facilitates absorption. of hydrogen sulphide. Where this is the case suitable means for releasing the absorbent liquid from the absorber I without nium phenolate or a solution of an ammo- `Patent 1,920,626.

nium or alkali metal salt of any tar acid other ,than phenolate. or a mixture of such salts. A preferred solution comprises a solution ordinarily containing by weight of NaOH and 15% by weight of a.' mixture of tar acids, principally phenol and cresol.

I may, however, employ other absorbent solutions such 'as a solution of sodium borate as set forth in the copending application of Gilbert A. Bragg, Serial No. 561,877, filed September 9, 1931,

Some hydrogen sulphide may be re My invention makes it possible to obtain hydrogen sulphide in substantially pure form in a simple and efficacious manner. 'I'he hydrogen sulphide thus recovered being free or substantially free from carbon dioxide and other impurities is suitable for the manufacture of sulphuric acid and other purposes in which hydrogen sulphide of a high degree of purity is required.

It will be apparent to those skilled in the art 10 that my invention is not limited to the specific details of operation or to the specific apparatus described hereinabove by way of illustration but may variouslybe practiced and embodied within the scope of the following claims.

I claim as my invention:

= 1. In a process of preferentially absorbing H28 from gaseous mixture containing relatively small amounts of carbon dioxide as compared to hydrogen sulphide for recovery therefrom of substantially pure HrS, the improvement which comi I; prises eecting the preferential absorption of H28 from said gas by washing thereof with a predominantly phenolic solution of alkali-forming metal compound and tar acid, of about a 10% 25 content by weight of the alkali anda 15% content by weight of tar acid and thereby selectively removing H23 preferentially from HzS and CO2 in the gas, heating the spent solution to liberate H28 preferentially absorbed thereby and 30 collecting the same, and thereby completing the recovering oi' the HzS of said gasas substantially pure HzS by preferential absorption thereof.

2. In a process of preferentially absorbing HzS from gaseous 4mixture containing at least twice 35 as much hydrogen sulphide as carbondioxide for recovery therefrom of substantially pure HzS, the improvement which comprises effecting the preferential absorption of Hzsjrom said gas by washing thereof with a predominantly phenolic o solution of alkali-forming metal compound and tar acid, of about a 10% content by weight of the alkali and a 15% content by weight of tar acid and thereby selectively removing Hzspreferentially fromHzS and. CO2 in the rgas, heating the 45 spent solution to liberate H2S preferentially absorbed thereby, precipitating incidental CO2 that may be present as an incident inthe preferentially absorbed I-IzS and collecting the HzS separately therefrom, and thereby completing the recovering of the HzS of said gas as substantially pure HzS by preferential absorption thereof.

3. In a process of preferentially absorbing HzS from gaseous mixture containing relatively small amounts of carbon dioxide as compared to hydominately phenolic' solution of about -a 10% so content by weight of NaOH and a 15% content by weight of tar acid and thereby selectively removing HzS preferentially from HzS and CO2 in the gas, heating .the spent solution to liberate HzS preferentially absorbed thereby and collecting the same, andthereby completing the recovering of the HzS of said gas as substantially pure HzS by preferential absorptio thereof.

4. In a process of preferentially absorbing HzS from gaseous mixture containing at least twice as much hydrogen sulphide as carbon dioxide for recovery therefrom of substantially pure HzS, the improvement which comprises effecting the preferential absorption of HzS from said gas by washing thereof with a predominantly phenolic solution of about a 10% content by weight-of NaOH and a 15% Ycontent by weight of tar acid and thereby 'selectively removing HzS preferentially from Has and CO2 in the gas, heating the spent solution to liberate HzS preferentially absorbed thereby, precipitating incidental CO2 that may be present as an incident in the preferentially absorbed HzS and collecting the HzS separately therefrom, and thereby completing the recovering of the HaS of said gas as substantially pure HzS by preferential absorption thereof.

5. In a process of manufacturing sulphuric acid the improvement which comprises preferentially absorbing H2S from gas mixtures containing relatively small amounts of carbon dioxide as com" pared to hydrogen sulphide by washing the gas mixture with a predominantly phenolic solution of alkali-forming metal compound and tar acid, of about a 10% content by weight of the alkali and a 15% content by weight of tar acid, heating the spent solution to liberate the HzS preferentially absorbed thereby as substantially pure Hi8, oxidizing .the sulphur of said HzS to sulphur dioxide, and converting said sulphur dioxide to sulphuric acid in the presence of oxides of nitrogen.

6. In a process oi' manufacturing sulphuric acid the improvement which comprises preferentially absorbing HzS relative to CO2 from gas mixtures containing relatively small amounts of carbon dioxide as compared to hydrogen sulphide by washing the gas mixture with a predominantly phenolic solution of alkali-forming metal compound and tar acid, the molar ratio of said alkali-forming metal to said tar acid in the solution being from 2:1 to 2:3, calculated as ROH (Where R represents alkali-forming metal) and tar acid, heating thewspent solution to' liberate the HzS preferentially absorbed thereby as substantially pure HzS, burning the HzS to sulphur dioxide, and catalytically converting said sulphur dioxide to sulphuric acid.

JOSEPH A. SHAW. 

